void setup(){
  Serial.begin(115200);

  Serial.println(rgbTo24BitHex(255, 255, 255)); //Print the string.
  //Serial.println(rgb565(0xFFFFFF),HEX);
}
void loop(){}
String rgbTo24BitHex(uint8_t Red, uint8_t Green, uint8_t Blue){
  char hex[] = {};
  //unsigned long result;
  sprintf(hex, "#%02X%02X%02X",Red, Green, Blue); //convert to an hexadecimal string. Lookup sprintf for what %02X means.
  //result = charHex2Hex(hex);
  return String(hex);
}
unsigned long charHex2Hex(char str[]){
  return strtol(str, 0, 16);
  //                  ^ = hexadecimal 
}
uint16_t rgb565(const unsigned long rgb)
{
  uint16_t R = (rgb >> 16) & 0xFF;
  uint16_t G = (rgb >>  8) & 0xFF;
  uint16_t B = (rgb      ) & 0xFF;

  uint16_t ret  = (R & 0xF8) << 8;  // 5 bits
           ret |= (G & 0xFC) << 3;  // 6 bits
           ret |= (B & 0xF8) >> 3;  // 5 bits
       
  return( ret);
}